It is known that an internal combustion engine of a motor vehicle includes at least a fuel injector for injecting a metered quantity of fuel into an engine cylinder, an intake valve for allowing an air quantity to mix with the fuel into the cylinder, and an exhaust valve for discharging the exhaust gas produced by the combustion of the air/fuel mixture inside the cylinder. The exhaust valve is in fluid communication with an aftertreatment system including an exhaust pipe and an oxygen concentration sensor (e.g. a lambda sensor or a nitrogen oxides NOx sensor) disposed in the exhaust pipe. The oxygen concentration sensor generates a signal (i.e. an electric signal) indicative of the oxygen concentration in the exhaust gas, which may be converted by an electronic control unit into a first signal representative of the air/fuel ratio of the mixture within the engine cylinder.
The electronic control unit may be also configured to generate a second signal representative of an expected air/fuel ratio inside the engine cylinder, which is not based on the signal coming from oxygen concentration sensor but estimated on the basis of the fuel injected quantity and on the air quantity delivered into the engine. This second signal is generally used to start many different control strategies of the internal control engine, in particular control strategies that make use of the aforementioned oxygen concentration sensor.
As a consequence, the reliability of these strategies generally depends on how the second signal generated by the electronic control unit actually adheres to the first signal generated with the aid of the oxygen concentration sensor.